This invention relates to a highway paving and coating machines and methods for their use and more particularly it relates to an apparatus and method for carrying the ingredients to a job site, and mixing and spreading the same for patching or coating a highway during any season of the year.
The need for patching and laying of roadway surfaces throughout the entire year has been a well known problem in the art. Generally, three different types of asphalt cement have been used. These are "hot," "cold cutback," and "cold emulsified" asphalts.
The purer the asphalt cement, the more dense and solid it is. In order for asphalt cement to be an effective binder in the production of asphalt concrete, it is necessary to transform it into a liquid state. In the case of "hot" asphalt paving materials, the more nearly pure asphalt cement is liquified by the use of heat up to as high as about 400.degree. F. In order to maintain the binding strength of the asphalt cement at the time of the production of the "hot" paving materials, the aggregates (stone, sand, and filler) must likewise be heated up to as high as about 500.degree. F. An example of a prior art apparatus designed to do this is shown in U.S. Pat. No. 3,820,914, which is directed to a self contained mobile asphalt mixing and applying apparatus. The entire disclosure of the aforementioned patent is incorporated herein by reference. This apparatus is suitable for producing a "hot" asphalt material for patching or resurfacing of a roadway during the late spring, summer and early fall months of the year. However, it is generally the practice of the asphalt paving materials industry to produce "cold" asphalt materials for "cold patch" purposes during the winter months when it is not practical to operate a "hot" asphalt concrete paving materials plant. This is because of the high heat requirements in order to keep the asphalt material liquid during the winter while it is in storage.
"Cold" asphalt cements have the advantage of not requiring great amounts of heat while stored during the winter months. "Cold" asphalt cement is available at all times throughout the year and can be stored in a liquid condition with relatively little expense. Such liquid asphalts cements are generally produced as a by-product during the refining of the almost pure asphalt cement used in the "hot" process.
"Cold" asphalting is usually accomplished by either of two general methods. First of all, in addition to the impurities of the asphalt cement that will keep it in the working state, "cutbacks," such as naptha, diesel fuel, and kerosene, may be added to reduce the viscosity of the asphalt cement so that it can be used without the extensive application of heat. Thus, "cold cutback" asphalt cement is available for using during the winter months. However, these materials suffer from the major disadvantage that the cutbacks are highly volatile and therefore, hazardous to handle. Additionally, they consume valuable petroleum resources, and during the process of placement and curing, release these cutbacks to the atmosphere to contribute to the general air pollution. Secondly, "cold emulsified" asphalt, which is a combination of asphalt, soap and water, may be manufactured by mixing asphalt cement at the refinery with a solution of soap and water to produce a liquid asphalt cement that is less hazardous to handle than the "cold cutback" asphalt cements. While "cold emulsified" asphalt cement has been available for almost 50 years, it has only been recently that the ionic exchange characteristics of the asphalt cement, as applied to asphalt concrete paving materials, are now known. Rapid curing (RC) asphalt cement is a type of emulsified asphalt cement with inhibitors added to correct the ionic exchange characteristics of asphalt cements that has not been subjected to heat in the process of producing the paving materials.
Thus, "cold patch" materials are stock piled for use during the entire year. In order to prevent the asphalt materials from "setting up" or otherwise curing in the stock pile so that they would be impossible to use during winter, other types of materials are often added. Consequently, the very items that are used to keep the "cold emulsified" asphalt from setting up or otherwise curing must be immediately dissipated by exposure to air and the heat of the sun in order for the asphalt concrete paving materials to be consolidated and remain in place. Unfortunately, this generally just does not happen and the "cold patch" materials soon erode from the areas of placement, such as potholes, and thus the entire purpose of using the same is defeated.
Even though while kept in storage, "cold emulsified" asphalt cement is kept liquid by minimal additions of heat and stirring during the coldest of winter months, most of the standards in the paving industry require the ambient temperature to be about 50.degree. F and rising before any of these materials should be applied to roadways.
Similar problems exist in the Portland Cement paving materials industry in that, as a general rule, Portland cement materials cannot be economically used for patching or resurfacing during the winter months.